IE7 requires html { font-size: 100%; } in establish-baseline()

I was checking out the updated vertical-rhythm module and saw that `* html { font-size: 100%; }` is only added for IE 6. I seemed to remember that IE 7 also required that. So I looked it up…

IE 6 and 7 cannot resize fonts set with px. http://alistapart.com/article/howtosizetextincss#section3

IE 6 and 7 resize fonts weirdly when set with em. http://alistapart.com/article/howtosizetextincss#section4

Since IE7 doesn't understand the `* html` selector hack, we have to switch to the `*property` hack that both IE 6 and IE 7 know (but IE 8 and above do not.)